A compact and thin-type image pickup device (which is also called a camera module, hereinafter) has come to be mounted on a mobile terminal representing a compact and thin-type electronic device such as a cell phone and PDA (Personal Digital Assistant), whereby, it has become possible to transmit mutually not only voice information but also image information to a remote location.
As image pickup elements used for these image pickup devices, a solid-state image pickup element such as an image sensor of a CCD type and an image sensor of a CMOS type are used. In recent years, increase of pixel numbers of the image pickup element have been advanced, and enhancement of its resolution and performance have been attained. As a lens for forming an image of a subject on the image pickup element, a lens made by resin that is suitable for mass production has come to be used for further cost reduction. A lens made of resin material has excellent workability and also has accurate transferability of a complicated shape of an aspheric surface, thus, it can cope also with an image pickup element with high resolution and high performance.
As an image pickup lens used in an image pickup device, there have been popularly known an optical system that is composed of lenses made of glass and an optical system that is composed of glass lenses and lenses made of resin material. Conventional optical systems are not enough to be used particularly for an image pickup device of a mobile terminal, and achieving both of much more compactness of the optical system and mass productivity required for the mobile terminal has been strongly demanded. However, it has been difficult to realize this requirement at low cost.
For overcoming the problem, there has been suggested the following method of manufacturing a large amount of camera modules. In the method, a large amount of arrayed lens elements are simultaneously formed through a replica method on a wafer in a size of several inches. After the wafer is joined with a sensor wafer, the joined body is cut to form a large amount of camera modules. Lenses manufactured by this method are sometimes called wafer-scale lenses, and camera modules manufactured by this method are sometimes called wafer-scale camera modules. Concerning such a technology, an image pickup lens in which a lens portion or lens portions are formed on a lens substrate is disclosed in each of Patent Literature 1 and Patent Literature 2.
Patent Literature 1: JP-A No. 2006-323365
Patent Literature 2: JP-B No. 3929479